Landslide

see also: Etymology of Landslide

A landslide is a geological phenomenon where a ground mass descends a slope, in other words a more or less continuous slip surface, more or less plane or curved. After the actuation the mass preserves overall its consistency and its aspect. It is thus always recognizable, which makes it possible to differentiate the landslides from the flow mud which do not have a clean form.

The landslides are only one type of gravitating movement (or movement of mass), however, by analogy with certain anglophone authors (English landslide), sometimes one improperly uses the term “landslide” to indicate any gravitating movement.

Factors:

a reduction in resistances of the ground ; the most frequent case is the reduction in the natural angle of repose of clays under the effect of water. In some rare cases, the latter is vaporized (because of the energies released by the very great masses concerned), its effect is then multiplied (proven with the crumbling of Granier of 1248).
a increase in the loads upstream , like the construction of a work,
a reduction in the supports in foot of slope , like a badly thought and too stiff earthwork, or on a scale different the withdrawal from a Glacier,
more rarely, a starting factor can intervene such as a vibration of machine, an explosion or a Séisme (to be noted that the seisms can be indirect factors, by reorganizing the flows of subsoil water).

This phenomenon is not to confuse with:

falls of coherent rocks, which are called “rock crumblings”;
collapses and depressions, whose total movement is not in conformity with the slope, and who are caused by ruptures of underground cavities;
the phenomena of withdrawal/swelling of some Clay S under the effect of the variations of moisture, where the movement is not either in conformity with the slope, and is reversible and nongravitating;
the volcanic phenomena, where the movements relate to Lave liquid and not of the ground S;
the Avalanche S of course which relate to the Neige and not the grounds, although the avalanche term of rock also exists.

The phenomena of erosion S under the effect of meteoric water (gullyings) are sometimes difficult to differentiate from the surface slips evolving/moving in flow mud; the criterion of differentiation relates to the existence of a movement of the significant ground before the phase of liquefaction in muddy casting.

Examples of landslide

563 or 564: crumbling of the Tauredunum, in the diocese of Were worth, in Suisse - its precise site was not elucidated, but of the campaigns of Géophysique in Léman recently accredited its existence, more probably locating it in valley of the Rhone.
November 24th 1248: crumbling of a section of the northern face of the Granier, in Savoy (between 1.000 and 5.000 dead), forming the undulating Vineyard S of the Abymes,
on April 26th, 1908, a slip which has occurred on argillaceous banks of the river of Hare, in the village of Our-Lady-of-the-Salette fact thirty three victims. Two days later, at the time of the funeral of 19 victims, 18 corpses always miss with the call. One can find in the 27,28,29 and April 30th, 1908 old editions of the newspaper the Fatherland available on the site of the Public records of Quebec, a series of reports, including/understanding photographs and sketches of this event.
on April 16th, 1970, a sanatorium of the plate of ESA was absorbed by a fatal mud flow
on May 5th, 1971, the village of St-Jean-Vianney to Quebec is carried in the mud of the Saguenay river. * In the night from January 7th to 8th 1994, the landslide of Room-in-Beaumont in the Isere (France) carries a million cubic meters in a few minutes and makes four victims,
Since the years 1980, the Ruines of Séchilienne go down slowly towards Romanche, in Isere, making fear a catastrophic crumbling,
February 17th 2006, Filipino: a mud flow crosses a village while making more than 300 died and 1500 missings in the east of the country.

Prevention

1/ The drainage: aim at limiting the water infiltrations in the ground. 2/ The vegetalisation: the plants, and in particular the roots, make it possible to stabilize the ground

See too

natural Risks - Catastrophe
Forest of protection - Akira Miyawaki

External bonds

Nearly 1.500 people is reported missing after a landslide in Philippines (LeMonde.fr Files, February 17th, 2006)
geology from Abymes de Myans

Simple: Landslide

Random links: